1. Field of the Invention
The present invention is a mechanical device to be used by trained medical physicians during medical procedures such as intubation of the trachea or other medical airway operations/procedures to maintain the cricoid pressure at a constant value during the procedure.
2. Prior Art
There are no known mechanical devices to assist a physician to maintain cricoid pressure during an endotracheal intubation or other related medical airway operation procedure. The only known method presently recognized or employed to maintain cricoid pressure during intubation of the trachea is to have a specially trained physician apply hand or finger pressure to the cricoid cartilage while an assisting physician completes the intubation. Endotracheal intubation involves advancing an endotracheal tube through the pharyngeal area into the trachea to ventilate the lungs.
Intubation of the trachea using various kinds of tracheal airways is frequently performed by medical personnel in a broad range of medical areas including anesthesiology, intensive and critical care, trauma surgery, emergency rooms, emergi-centers, and pre-hospital care. After successful intubation, the patient is ventilated with manual or mechanical air supplies.
There is a high risk of aspiration of gastric contents into the lungs during intubation or cricothyroidotomies because the cricoid pressure increases and thereby creates an imbalance between the lungs, stomach and interconnected passages. This imbalance causes gastric contents to be aspirated into the lungs, and resulting aspiration pneumonitis, which most often is fatal to the patient. The solution of the problem is to precisely manipulate and maintain cricoid pressure to counteract reduction in esophageal sphincter pressure (OSP) and prevent regurgitation into the lungs, during intubation.
Recent medical literature recognizes that gastric aspiration is a frequently encountered problem, and strongly recommends application of cricoid pressure on all patients during these procedures. However, practitioners do not have a mechanical device available to properly measure, manipulate or maintain the cricoid cartilage pressure. The recommended procedure is to have a physician apply the proper amount of pressure until the airway is properly placed. Medical attendants employing this technique are carefully trained to be able to guess or estimate the amount of pressure being applied to the cricoid cartilage by hand and finger pressure on the patient's trachea. The proper cricoid pressure is known to be between 27 to 30 newtons for a conscious patient and between 38 to 40 for an unconscious patient. The trained attending physician is supposed to be able to estimate, due to his training, and to maintain the precise force as intubation is occurring without distortion of the trachea. Unfortunately, too much or too little force/pressure may put the patient at risk. The two-fold risk is from: too much pressure which may damage the trachea or surrounding anatomical structures and distort the airway thereby producing inadequate patient ventilation; or, too little pressure, which obviates the efficacy of the procedure by failing to alter esophageal pressure enough to prevent aspiration of gastric contents.
Studies performed at St. Thomas Hospital, London, England and published in Anesthesiology 1992, V47 indicate the absolute necessity of maintaining proper levels of cricoid pressure needed during intubation procedures. That article indicates that the only `safe` method is to use two medical attendants, one to apply the cricoid pressure and the other to perform the intubation. The article also identifies the exact pressure to be applied to the cricoid, but does not propose any method for measuring or maintaining that pressure.
In the Journal of the American Medical Association Standards for CPR and ECC, page 2935, the procedure to performing intubation is specified:
"Cricoid pressure requires a second person and should be applied, when possible, during endotracheal intubation to protect against regurgitation of gastric contents, as follows: to find the anatomic landmark, palpate the depression just below the thyroid cartilage (Adam's apple). This depression is the cricothyroid membrane; the prominence inferior to that is the cricoid cartilage. Pressure should be applied to the anterolateral aspects of the cartilage just lateral to the midline. This pressure is applied with the thumb and index fingers of either hand. A higher degree of pressure is required to prevent regurgitation than to prevent gastric distention. The pressure on the cricoid should be maintained until the cuff of the endotracheal tube is inflated." (Standards for CPR and ECC, JAMA, Vol. 255. No. 21, p. 2935.) PA1 Because of the high risk of aspiration pneumonitis, all pregnant patients receiving general anesthesia must be considered to have a full stomach. Therefore, use of a rapid-sequence induction, with cricoid pressure until the airway has been secured with a cuffed endotracheal tube, is preferred.
In Anesthesia, by Ronald D. Miller, M.D. Vol 2, some of the attendant problems and solutions are identified.
"Cricoid pressure is the simplest and most effective measure for minimizing the risk of aspiration. However, the person applying cricoid pressure must know how to do so properly. Pressure is applied at the cricoid cartilage, not the thyroid cartilage or over the entire larynx. Pressure applied to the thyroid cartilage makes the intubation process more difficult, whereas pressure applied to the cricoid cartilage makes endotracheal intubation easier. Some prefer to place one hand behind the patient's neck while applying pressure at the cricoid cartilage. In addition to ensuring proper placement of pressure, the attendant must not release the pressure until the intubation is complete and the cuff inflated.
It is very tempting when things go awry during rapid sequence induction for the attendant applying cricoid pressure to help by picking up a dropped endotracheal tube, finding a stylet, correcting an intravenous needle placement, or even removing false teeth or other material from the mouth. It is at this precise time that regurgitation and aspiration can and most likely will occur. Maternal mortality studies from England demonstrate that in 7 or 11 cases of aspiration that occurred during caesarean section, the person applying cricoid pressure had applied it inappropriately or had released it before the intubation was complete. Applied properly, cricoid pressure should prevent nearly all cases of aspiration." (Management of Aspiration Pneumonitis, Gibbs and Modell, p. 1311.)
In the Medical Journal Digest Volume 75, May 5, 1979, a study to evaluate intubation indicated that: "the department or level of training of the intubator did not affect the ratio of complications . . . " It is obvious that even a trained physician can not apply and maintain the proper pressure without some method of determining the cricoid pressure during intubation.
In Respiratory Care, 1990, 5th edition, page 450, it was noted:
One out of three patients with gross aspiration that progresses to pneumonia will die as a result of that condition.
Eighty percent (80%) of all patients with tracheostomies have one or more episodes of aspiration . . .
Massive aspiration leads to cardiac arrest . . .
Intubation is a very advanced medical procedure that can result in severe harm to a patient, should things go wrong. The problem of measuring and maintaining cricoid pressure has been identified. The present invention overcomes all of these problems by providing an accurate, reliable mechanical device capable of exerting and maintaining precise cricoid pressure during the entire intubation process. It also permits the procedure to be completed by one physician.